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package bjc.utils.parserutils;
import java.util.Deque;
import java.util.LinkedList;
import java.util.function.Function;
import java.util.function.Predicate;
import bjc.utils.data.IHolder;
import bjc.utils.data.IPair;
import bjc.utils.data.ITree;
import bjc.utils.data.Identity;
import bjc.utils.data.Pair;
import bjc.utils.funcdata.IList;
/**
* Creates a parse tree from a postfix expression
*
* @author ben
*
*/
public class TreeConstructor {
/**
* Alias interface for special operator types.
*
* @param <TokenType>
* The token type of the tree.
*/
public interface QueueFlattener<TokenType> extends Function<Deque<ITree<TokenType>>, ITree<TokenType>> {
}
/*
* Alias for constructor state.
*/
static final class ConstructorState<TokenType> extends Pair<Deque<ITree<TokenType>>, ITree<TokenType>> {
public ConstructorState(final Deque<ITree<TokenType>> left, final ITree<TokenType> right) {
super(left, right);
}
public ConstructorState(final IPair<Deque<ITree<TokenType>>, ITree<TokenType>> par) {
super(par.getLeft(), par.getRight());
}
}
/**
* Construct a tree from a list of tokens in postfix notation
*
* Only binary operators are accepted.
*
* @param <TokenType>
* The elements of the parse tree
* @param tokens
* The list of tokens to build a tree from
* @param isOperator
* The predicate to use to determine if something is a
* operator
* @return A AST from the expression
*/
public static <TokenType> ITree<TokenType> constructTree(final IList<TokenType> tokens,
final Predicate<TokenType> isOperator) {
/*
* Construct a tree with no special operators
*/
return constructTree(tokens, isOperator, op -> false, null);
}
/**
* Construct a tree from a list of tokens in postfix notation.
*
* Only binary operators are accepted by default. Use the last two
* parameters to handle non-binary operators.
*
* @param <TokenType>
* The elements of the parse tree.
*
* @param tokens
* The list of tokens to build a tree from.
*
* @param isOperator
* The predicate to use to determine if something is a
* operator.
*
* @param isSpecialOperator
* The predicate to use to determine if an operator needs
* special handling.
*
* @param handleSpecialOperator
* The function to use to handle special case operators.
*
* @return A AST from the expression
*
*/
public static <TokenType> ITree<TokenType> constructTree(final IList<TokenType> tokens,
final Predicate<TokenType> isOperator, final Predicate<TokenType> isSpecialOperator,
final Function<TokenType, QueueFlattener<TokenType>> handleSpecialOperator) {
/*
* Make sure our parameters are valid
*/
if (tokens == null)
throw new NullPointerException("Tokens must not be null");
else if (isOperator == null)
throw new NullPointerException("Operator predicate must not be null");
else if (isSpecialOperator == null)
throw new NullPointerException("Special operator determiner must not be null");
/*
* Here is the state for the tree construction
*/
final IHolder<ConstructorState<TokenType>> initialState = new Identity<>(
new ConstructorState<>(new LinkedList<>(), null));
/*
* Transform each of the tokens
*/
tokens.forEach(new TokenTransformer<>(initialState, isOperator, isSpecialOperator,
handleSpecialOperator));
/*
* Grab the tree from the state
*/
return initialState.unwrap(pair -> {
return pair.getRight();
});
}
}
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